1. Technical Field of the Invention
This invention relates to intraocular lenses (IOLs), which are to be implanted in the eye to replace a natural lens that has been removed because of cataract or other reasons. More particularly, this invention relates to an IOL with an uniquely-shaped support loop or haptic designed to be implanted in the posterior chamber of the eye.
2. Background of the Invention
There are many IOLs of varied shapes on the market, which are used to replace the natural lens of the eye after extra-capsular surgery where the natural lens of the eye is removed. Such lenses include an optical portion and one or more support loops or haptics, which retain the IOL optic in the eye in its desired position either in front of the iris in the anterior chamber or to the rear of the iris in the posterior chamber.
The support loops retain the IOL in a relatively fixed position so that light can be focused on the retina. It is advantageous for the support loops to be flexible in order to accommodate changes in shape of the eyeball without causing damage to any of the interior portions of the eye in contact with the support loops.
IOLs can be formed of a single-piece of material such as polymethylmethacrylate (PMMA) where the support loops are formed integral with the optic portion through casting, machining or lathe cutting methods. Other types of IOLs, called multi-piece lenses, can also be formed where support loops made of a material such as polypropylene or PMMA (VS-100) are attached to an optic portion by heat welding or through laser welding, ultrasonic welding or other methods.
Haptics can be formed of a stiff material, but they are more often flexible in order to facilitate positioning of the lens in the proper location while accommodating for changing shapes of the eyeball. The haptic design, including its flexibility, is considered to be important in achieving maximum patient comfort and lack of post-operative complications, ease of implantation and effectiveness of maintaining the lens in its proper position.
Haptic shape is also an important consideration in connection with surgical procedures and the size of an incision in the eye through which an IOL can be inserted. Smaller incisions are desirable in order to reduce astigmatic effects caused by distortion of the eyeball after surgery is completed. For IOLs with optics formed of a relatively stiff material, it is desirable for haptics to be designed so that they can be manipulated to overlap the optic portion during insertion so the incision can be formed only slightly larger than the optic diameter.
Typically, haptics are constructed so as to generate a reactive force as a result of any movement of the IOL in the eye. This reactive force has an axial component that assists to some extent in maintaining an IOL in its proper axial position relative to the plane of the optic. Also, the reactive force has a radial component directed toward the center of the optic which tends to maintain the lens in its proper radial position in order to insure proper image projection on the retina. This radial component must be great enough to hold the lens in position and small enough to allow the haptics to flex without causing irritation to the eye structure. Thus, haptics must be sufficiently flexible to generate these reactive forces in the proper amount regardless of the changes in the shape of the eye.
Currently known haptic designs do not achieve optimum reactive force in the radial or axial directions. Because of the orientation of the haptics relative to an optic and because of the shape and the length of the support loops themselves, contact points between the support loops and surrounding eye structure are to some degree limited to a narrow sector that extends radially outward from the center of the lens with respect to the attachment point of the support loop on the periphery of the optic. As a result, lenses that are too flexible can become de-centered where the radial reactive force is not sufficient to maintain the lens in its proper position as the eyeball distorts.
Another problem in connection with the fabrication of IOLs is that some physicians prefer lenses where the support loops are formed coplanar with the optic, while others believe that IOLs with support loops designed to project at an angle relative to the plane of the optic are desirable. For most multipiece IOLs of this nature, the manufacturing process must be altered in order to fabricate a lens with angled support loops by drilling the holes in the optic at this angle, into which the support loops are inserted. This complicates the manufacturing process since a different tooling and technique for drilling holes for these angled haptics is required than for the ones coplanor with the optic. Also, this complicates an inventory since plano and angled optics must be built and stored separately.
An example of an IOL that is considered to provide beneficial characteristics for implantation in the posterior chamber has support loops that are open ended and project radially outwardly from opposite sides of an optic. Such lenses are commonly referred to as J-loop or C-loop lenses, or the like, and are characterized by a curved-loop configuration that ends at a point spaced from the periphery of the optic portion. A number of variations of this lens style have curved loops with varying degrees of contact with the interior of the eye.
The loops can be manipulated to overlap the optic during insertion to minimize the length of an incision. However, because of the long shape of the loops they are believed to be overly flexible and tend to de-center in the eye after implantation. Further, in order to form lenses with such loops where the loops are oriented at an angle relative to the plane of the optic, holes must be drilled in the optic at that angle instead of in the planar direction.